Mobile Internet - devices, technologies, subtleties. How GSM networks work or a brief communication basics Communication channels in cell phones

To do this, we suggest you go to the "Beeline" company.

A huge number of BS - base stations are installed on the territory of Russia. Probably, many of you yourself have seen red and white structures towering in the fields or structures installed on the roofs of non-residential buildings. Each such base station is capable of picking up a signal from a cell phone at a distance of up to 35 km, communicating with it via service or voice channels.

After you have dialed the number of the desired subscriber on your phone, the following happens: the mobile phone finds the nearest base station, contacts it via the service channel and requests a voice channel. After that, the BS sends a request to the controller (BSC), which then goes to the communicator. If the called subscriber is served by the same operator as you, the communicator will check the Home Location Register (HLR) database to find out exactly where the person you are calling is and will redirect the call to the correct switch, which will then transfer the call to the controller and then to the Base Station. Finally, the Base Station will contact the person's mobile phone and connect you to it. And if the person with whom you want to talk is a subscriber of another cellular operator, or you call a city number, the switch will “find” the corresponding switch of the other network and contact him. Sounds confusing enough, right? Let's try to analyze this issue in more detail.

But back to the hardware. As we already said, from the BS, the call is transferred to the controller (BSC). Outwardly, it differs little from the Base Station:

The number of BSs that the controller is able to service can reach six dozen. The controller and BS communicate via optical or radio relay channels. The controller controls the operation of radio channels.

Below you can see what the switch is:

The number of controllers supported by the switch varies from two to thirty. Switches are placed in large rooms filled with metal equipment cabinets.

The switch's job is to manage traffic. If earlier, in order to talk to each other, subscribers had to first contact the telephone operator, who then manually rearranged the necessary wires, now the switch is doing a great job with her role.

Inside the cars there are devices for reading and processing data:

Controllers and switches are monitored 24 hours a day. Tracking is conducted in the so-called CCS (Flight Control Center of the Network Control Center).

Cellular communications are considered one of the most useful inventions of mankind - along with the wheel, electricity, the Internet and the computer. And in just a few decades, this technology has gone through a number of revolutions. How did wireless communication begin, how cells work and what opportunities the new mobile standard will open 5G?

The first use of mobile telephone radio communications dates back to 1921, when Detroit police used one-way dispatcher communication in the 2 MHz band in the United States to transmit information from a central transmitter to receivers in police cars.

How cellular communication appeared

For the first time the idea of \u200b\u200bcellular communication was put forward in 1947 - worked on it by engineers from Bell Labs Douglas Ring and Ray Young. However, the real prospects for its implementation began to emerge only in the early 1970s, when the company's employees developed the working architecture of the cellular hardware platform.

For example, American engineers proposed to place transmitting stations not in the center, but at the corners of the "cells", and a little later a technology was invented that would allow subscribers to move between these "cells" without interrupting communications. After that, it remains to develop operating equipment for this technology.

The problem was successfully solved by Motorola - its engineer Martin Cooper demonstrated the first working prototype of a mobile phone on April 3, 1973. He called the head of the research department of a competitor company directly from the street and told him about his own successes.

Motorola's management immediately invested $ 100 million in a promising project, but the technology entered the commercial market only ten years later. This delay is due to the fact that it was first required to create a global infrastructure of cellular base stations.

In the United States, AT&T took over this work - the telecommunications giant obtained licensing of the necessary frequencies from the federal government and built the first cellular network that covered the largest American cities. The famous Motorola DynaTAC 8000 was the first mobile phone.

The first cell phone went on sale on March 6, 1983. It weighed almost 800 grams, could work on a single charge for 30 minutes of talk time and charged for about 10 hours. At the same time, the device cost $ 3995 - a fabulous sum for those times. Despite this, the mobile phone instantly became popular.

Why is the connection called cellular

The principle of mobile communication is simple - the territory where the connection of subscribers is provided is divided into separate cells or "cells", each of which is served by a base station. At the same time, in each "cell" the subscriber receives identical services, so he himself does not feel the crossing of these virtual boundaries.

Usually a base station in the form of a pair of iron cabinets with equipment and antennas is placed on a specially built tower, but in the city they are often placed on the roofs of high-rise buildings. On average, each station picks up a signal from mobile phones at a distance of up to 35 kilometers.

To improve the quality of service, operators are also installing femtocells - low-power and miniature cellular stations designed to serve a small area. They allow to dramatically improve coverage in places where it is needed. Cellular communications in Russia will be combined with space

The mobile phone in the network listens to the air and finds the signal of the base station. In addition to the processor and RAM, a modern SIM card has a unique key that allows you to log in to the cellular network. The phone can communicate with the station using different protocols - for example, digital DAMPS, CDMA, GSM, UMTS.

Cellular networks of different operators are connected to each other, as well as to the landline telephone network. If the phone leaves the range of the base station, the device establishes communication with others - the connection established by the subscriber is invisibly transmitted to other "cells", which ensures continuous communication when moving.

In Russia, three bands are certified for broadcasting - 800 MHz, 1800 MHz and 2600 MHz. The 1800 MHz band is considered the most popular in the world as it combines high capacitance, long range and high penetration. It is in it that most mobile networks now work.

What mobile communication standards are

The first mobile phones worked with 1G technologies - this is the very first generation of cellular communications, which was based on analog telecommunication standards, the main of which was NMT - Nordic Mobile Telephone. It was intended solely for the transmission of voice traffic.

The birth of 2G dates back to 1991 - GSM (Global System for Mobile Communications) became the main standard of the new generation. This standard is still supported. Communication in this standard became digital, it became possible to encrypt voice traffic and send SMS.

The data transfer rate within GSM did not exceed 9.6 kbps, which made it impossible to transmit video or high-quality audio. The GPRS standard known as 2.5G was intended to solve the problem. For the first time, it allowed mobile phone owners to use the Internet.

This standard has already provided data transfer rates of up to 114 Kbps. However, it soon ceased to satisfy the ever-growing user demands. To solve this problem, the 3G standard was developed in 2000, which provided access to the Network services at a data transfer rate of 2 Mbit.

Another difference of 3G was the assignment of an IP address to each subscriber, which made it possible to turn mobile phones into small computers connected to the Internet. The first commercial 3G network was launched on October 1, 2001 in Japan. In the future, the throughput of the standard has repeatedly increased.

The most up-to-date standard is fourth-generation 4G communication, which is intended only for high-speed data services. The bandwidth of the 4G network is capable of reaching 300 Mbit / s, which gives the user almost unlimited opportunities to surf the Internet.

Cellular communication of the future

The 4G standard is sharpened for the continuous transfer of gigabytes of information, it does not even have a channel for voice transmission. Due to extremely efficient multiplexing schemes, downloading a high-definition movie on such a network will take the user 10-15 minutes. However, even its capabilities are already considered limited.

In 2020, the official launch of a new generation of 5G communication is expected, which will allow the transfer of large amounts of data at ultra-high speeds up to 10 Gbps. In addition, the standard will allow connecting up to 100 billion devices to high-speed Internet.

It is 5G that will allow the true Internet of Things to appear - billions of devices will exchange information in real time. According to experts, network traffic will soon grow by 400%. For example, cars will start to constantly be in the global network and receive data on traffic conditions.

The low latency will ensure real-time communication between vehicles and infrastructure. A reliable and always-on connection is expected to open up the possibility for fully autonomous vehicles to run on the roads for the first time.

Russian operators are already experimenting with new specifications - for example, Rostelecom is working in this direction. The company signed an agreement to build 5G networks at the Skolkovo innovation center. The project is part of the state program "Digital Economy", recently approved by the government.

Millions of people around the world use mobile phones because mobile phones have made it much easier to communicate with people around the world.

Mobile phones present a whole range of functions these days, and there are more and more of them every day. Depending on your mobile phone model, you can do the following:

Save important information
Take notes or make a list of tasks
Record important appointments and turn on an alarm for reminders
use a calculator for calculations
send or receive mail
search for information (news, statements, anecdotes and much more) on the Internet
play games
watch TV
send messages
use other devices such as MP3 player, PDA devices and GPS navigation system.

But haven't you ever wondered how a mobile phone works? And what makes it different from a simple landline phone? What do all these terms PCS, GSM, CDMA and TDMA mean? This article will focus on the new capabilities of mobile phones.

To begin with, a mobile phone is essentially a radio - a more advanced form, but a radio nonetheless. The telephone itself was created by Alexander Graham Bell in 1876, and wireless communication a little later by Nikolai Tesla in the 1880s (the Italian Guglielmo Marconi first started talking about wireless communication in 1894). It was destined for these two great technologies to come together.

In ancient times, when there were no mobile phones yet, people installed radio phones in their cars to communicate. This radiotelephone system was powered by a single main antenna mounted on a tower in the city border and supported about 25 channels. To connect to the main antenna, the phone had to have a powerful transmitter - with a radius of about 70 km.

But not many could use such radio phones due to the limited number of channels.

The genius of the mobile system lies in the division of the city into several elements ("honeycomb"). This promotes frequency reuse throughout the city, so millions of people can use mobile phones at the same time. "Honeycomb" was not chosen by chance, since it is precisely honeycombs (in the form of a hexagon) that can best cover the area.

In order to better understand the operation of a mobile phone, it is necessary to compare CB radio (i.e. conventional radio) and a radiotelephone

Full duplex handheld versus half duplex - a radiotelephone, like a simple radio, is a half duplex device. This means that two people are using the same frequency, so they can only speak in turn. A mobile phone is a full duplex device, which means that a person uses two frequencies: one frequency is for hearing the person on the other side, the other for talking. Therefore, you can talk on mobile phones at the same time.

Channels - the radiotelephone uses only one channel, in the radio there are about 40 channels. A simple mobile phone can have 1,664 channels or more.

In half-duplex devices, both radio transmitters use the same frequency, so only one person can speak. In full duplex devices, the 2 transmitters use different frequencies, so people can talk at the same time. Mobile phones are considered full duplex devices.

In a typical US mobile system, a mobile phone user uses about 800 frequencies to talk around the city. A mobile phone divides the city into several hundred. Each cell is of a certain size and covers an area of \u200b\u200b26 km2. Honeycombs are like hexagons enclosed in a lattice.

Since mobile phones and stations use low power transmitters, non-adjacent cells can use the same frequencies. Two cells can use the same frequencies. The cellular network is powerful high-speed computers, base stations (multi-frequency VHF transceivers), distributed throughout the entire working area of \u200b\u200bthe cellular network, mobile phones and other high-tech equipment. We'll talk about base stations later, but now let's look at the "cells" that make up the cellular system.

One cell in an analog cellular system uses 1/7 of the available two-way communication channels. This means that each cell (out of 7 cells in the lattice) uses 1/7 of the available channels, which have their own set of frequencies and, due to this, do not overlap:

A mobile phone user usually receives 832 radio frequencies for city calls.
Each mobile phone uses 2 frequencies per call - the so-called. two-way channel - therefore, there are 395 communication channels for each mobile phone user (the remaining 42 frequencies are used by the main channel - we will talk about it later).

Thus, each cell has up to 56 available communication channels. This means that 56 people will be able to talk on their mobile phones at the same time. The first mobile technology 1G is considered an analogue of the cellular network. Since the introduction of digital transmission of information (2G), the number of channels has increased significantly.

Mobile phones have built-in low-power transmitters, so they work at 2 signal levels: 0.6 watts and 3 watts (for comparison, we will give a simple radio that operates at 4 watts). Base stations also use low-power transmitters, however, they have their advantages:

The transmission of the signal of the base station and the mobile phone within each cell does not allow you to go far from the cell. In this way, both cells can reuse the same 56 frequencies. The same frequencies can be used throughout the city.
The charge consumption of a mobile phone, which usually runs on battery power, is not significantly high. Low-power transmitters mean a small battery, which makes mobile phones more compact.

The cellular network needs a number of base stations, regardless of the size of the city. A small town should have several hundred towers. All mobile phone users in any city are managed by one main office, which is called the Mobile Telephone Switching Center. This center monitors all telephone calls and base stations in the area.

Mobile phone codes

The Electronic Serial Number of the Device (ESN) is a unique 32-bit number programmed into the mobile phone by the manufacturer.
Mobile Identification Number (MIN) is a 10-digit code derived from the mobile phone number.
The System Identification Code (SID) is a unique 5-digit code that is assigned to each FCC company. The last two codes, MIN and SID, are programmed into your mobile phone when you buy a card and turn on the phone.

Each mobile phone has its own code. Codes are needed to recognize phones, mobile phone owners and mobile operators. For example, you have a mobile phone, you turn it on and try to call. Here's what happens at this time:

When you just turn on the phone, it looks for an identification code on the main control channel. A channel is a special frequency that mobile phones and base stations use to transmit signals. If the phone cannot find the control channel, then it is out of reach and the message "no network" is displayed on the screen.
When the phone receives an identification code, it verifies it against its own code. If matched, the mobile phone is allowed to connect to the network.
Together with the code, the phone requests access to the network and the Mobile Phone Switching Center records the position of the phone in the database, so the Switching Center knows which phone you are using when it wants to send you a service message.
The switching center receives calls and can figure out your number. At any time, he can view your phone number in his database.
The switching center communicates with your mobile phone to tell you which frequency to use, and after the mobile phone connects to the antenna, the phone gains access to the network.

The cell phone and base station maintain constant radio contact. The cell phone periodically switches from one base station to another with a stronger signal. If the cell phone leaves the base station field while moving, then it establishes communication with another, nearest base station, even during a conversation. The two base stations "communicate" through the Switching Center, which sends a signal to your mobile phone to change the frequency.

There are times when, while moving, the signal moves from one cell to another belonging to another mobile operator. In this case, the signal does not disappear, but is transmitted to another mobile operator.

Most modern cell phones can operate in several standards, which makes it possible to use roaming services on different cellular networks. The wiring center you now use the cellphone connects to your wiring center and asks for a code confirmation. Your system transfers all data about your phone to another system and the Switching Center connects you to the cells of the new mobile operator. And the most amazing thing is that all this is done within a few seconds.

The most unpleasant thing about all this is that you can pay a tidy sum for roaming calls. On most phones, when you just cross the border, the roaming service is displayed. Otherwise, you'd better check the mobile coverage map so that you don't have to pay "inflated" tariffs later. Therefore, check immediately the cost of this service.

Please note that the phone must operate in multiple bands if you want to use the roaming service, because different countries use different bands.

In 1983, the first analogue mobile standard, AMPS (Advanced Mobile Telephone Service), was developed. This analog mobile communication standard operates in the frequency range from 825 to 890 MHz. In order to maintain competition and keep prices in the marketplace, the US federal government required that there be at least two companies in the market, engaged in the same activity. One such company in the United States was the Local Telephone Company (LEC).

Each company had its own 832 frequencies: 790 for calls and 42 for data. To create one channel, two frequencies were used at once. The frequency range for an analog channel was typically 30 kHz. The range of transmission and reception of the voice channel is divided by 45 MHz, so that one channel does not overlap with another.

A version of the AMPS standard called NAMPS (Narrowband Advanced Communications System) uses new digital technologies to enable the system to triple its capabilities. But even despite the fact that it uses new digital technologies, this version remains just an analogue. Analog standards AMPS and NAMPS only operate at 800 MHz and cannot yet offer a wide variety of functions, such as Internet connection and mail handling.

Digital mobile phones are second generation (2G) mobile technologies. They use the same radio technology as analog phones, albeit in a slightly different way. Analog systems do not fully utilize the signal between the phone and the mobile network — analog signals cannot be suppressed or manipulated as easily as digital signals can. This is one of the reasons why many cable companies are migrating to digital, so they can use more channels in a given range. It's amazing how efficient a digital system can be.

Many digital mobile systems use frequency modulation (FSK) to transmit and receive data through the analog AMPS portal. Frequency modulation uses 2 frequencies, one for logic one and one for logic zero, choosing between the two when transmitting digital information between the tower and the mobile phone. In order to convert analog information into digital and vice versa, modulation and coding scheme are needed. This suggests that digital mobile phones need to be able to process data quickly.

In terms of "complexity per cubic inch," mobile phones are among the most sophisticated devices available today. Digital mobile phones can perform millions of calculations per second in order to encode or decode a voice stream.

Any ordinary phone consists of several parts:

Microcircuit (board), which is the brain for the phone
Antenna
Liquid crystal display (LCD)
Keyboard
Microphone
Speaker
Battery

The microcircuit is the center of the entire system. Next, we will look at what chips are there and how each of them works. A chip for converting analog information to digital and vice versa encodes the outgoing audio signal from the analog system to digital and the incoming signal from the digital system to the analog system.

A microprocessor is a central processing unit responsible for the bulk of information processing. It controls the keyboard and display, and many other processes.

The ROM chips and memory card chip can store the operating system data of the mobile phone and other user data such as phone book data. Radio frequency manages power and charge, and also works with hundreds of FM waves. The RF amplifier controls the signals that enter or reflect the antenna. The screen size has increased significantly since the mobile phone has more features. Many phones have notebooks, calculators, and games. And now many more phones connect to a PDA or Web browser.

Some phones store certain information, such as SID and MIN codes, in the built-in flash memory, while others use external cards such as SmartMedia cards.

Many phones have speakers and microphones so tiny that it's hard to imagine how they make any sound at all. As you can see, the speakers are the same size as a small coin, and the microphone is no bigger than a watch battery. By the way, such wristwatch batteries are used in the internal chip of a mobile phone to operate the watch.

The most amazing thing is that 30 years ago, many such details occupied an entire floor of a building, and now all this fits in the palm of a person.

There are three most common ways 2G mobile phones use radio frequencies to transmit information:

FDMA (English Frequency Division Multiple Access) TDMA (English Time Division Multiple Access) CDMA (English Code Division Multiple Access) - Code Division Multiple Access.

Although the names of these methods seem so confusing, you can easily guess how they work by simply breaking the name into separate words.

The first word, frequency, time, code, indicates the accessor method. The second word, division, refers to the fact that it separates calls based on the access method.

FDMA places each call on a separate frequency TDMA allocates a certain time to each call on the specified frequency CDMA assigns a unique code to each call and then transmits it to a free frequency.

The last word of each method “multiple” means that several people can use each cell.

FDMA

FDMA (Frequency Division Multiple Access) is a method of using radio frequencies, when there is only one subscriber in one frequency range, different subscribers use different frequencies within a cell. It is an application of frequency division multiplexing (FDM) in radio communications. In order to better understand how FDMA works, it is necessary to consider how radios work. Each radio station sends its signal to free frequency bands. The FDMA method is used primarily for the transmission of analog signals. And although this method can undoubtedly transmit digital information, it is not used, since it is considered less effective.

TDMA

TDMA (Time Division Multiple Access) is a method of using radio frequencies, when there are several subscribers in the same frequency slot, different subscribers use different time slots (slots) for transmission. It is an application of time division multiplexing (TDM) to radio communications. With TDMA, the narrow bandwidth (30 kHz wide and 6.7 milliseconds long) is split into three time slots.

Narrow bandwidth is commonly referred to as “channels”. Voice data converted into digital information is compressed so it takes up less space. Therefore, TDMA operates three times faster than an analog system using the same number of channels. TDMA systems operate on the 800 MHz (IS-54) or 1900 MHz (IS-136) frequency bands.

GSM

TDMA is currently the dominant technology for mobile cellular networks and is used in the GSM (Global System for Mobile Communications) (Russian SPS-900) standard - a global digital standard for mobile cellular communications, with channel division according to the TDMA principle and a high degree of security due to public key encryption. However, GSM uses TDMA and IS-136 access differently. Let's imagine that GSM and IS-136 are different operating systems that run on the same processor, for example, both Windows and Linux operating systems are based on Intel Pentium III. GSM systems use a coding method to encrypt phone calls from mobile phones. The GSM network in Europe and Asia operates at 900 MHz and 1800 MHz, and in the USA at 850 MHz and 1900 MHz and is used for mobile communications.

Blocking your GSM phone

GSM is an international standard in Europe, Australia, most of Asia and Africa. Mobile phone users can buy one phone that will work wherever this standard is supported. In order to connect to a specific mobile operator in different countries, GSM users simply change their SIM card. SIM cards store all information and identification numbers that are required to connect to a mobile operator.

Unfortunately, the 850MHz / 1900-MHz GSM frequencies used in the United States do not match those of the international system. Therefore, if you live in the USA, but you really need a mobile phone abroad, you can buy a three- or four-band GSM phone and use it at home and abroad, or just buy a mobile phone with GSM 900MHz / 1800MHz standard to travel abroad. ...

CDMA

CDMA (Code Division Multiple Access). Traffic channels with this method of dividing the medium are created by assigning each user a separate numeric code that spreads across the entire bandwidth. There is no time division, all subscribers constantly use the entire channel bandwidth. The frequency band of one channel is very wide, the subscribers' broadcasting overlaps each other, but since their codes are different, they can be differentiated. CDMA is the basis for IS-95 and operates in the 800 MHz and 1900 MHz bands.

Dual band and dual standard mobile phone

When you travel to travel, you undoubtedly want to find a phone that will work on several lanes, in several standards, or will combine both. Let's take a closer look at each of these possibilities:

A multiband phone can switch from one frequency to another. For example, a dual band TDMA telephone can use TDMA services in an 800 MHz or 1900 MHz system. A dual-band GSM phone can use the GSM service in three bands - 850 MHz, 900 MHz, 1800 MHz or 1900 MHz.
Multi-standard telephone. "Standard" in mobile phones means the type of signal transmission. Therefore, a phone with AMPS and TDMA standards can switch from one standard to another if necessary. For example, the AMPS standard allows you to use the analogue network in areas where the digital network is not supported.
The multiband / multistandard phone allows you to change the frequency band and transmission standard.

Phones that support this feature automatically change bands or standards. For example, if the phone supports two bands, then it connects to the 800 MHz network, if it cannot connect to the 1900 MHz band. When a phone has several standards, it first uses a digital standard, and if it is not available, it switches to an analog one.

Mobile phones come in two and three bands. However, the word "three-lane" can be deceiving. It can mean that the phone supports CDMA and TDMA standards, and an analog standard. And at the same time, it can mean that the phone supports one digital standard in two bands and an analog standard. For those traveling abroad, it is better to get a phone that operates on the 900 MHz GSM band for Europe and Asia and 1900 MHz for the US, and also supports the analog standard. In essence, it is a dual band phone with one of these modes (GSM) supporting 2 bands.

Cellular and Personal Communications Service

Personal Communications Service (PCS) is essentially a mobile phone service that emphasizes personal communications and mobility. The main feature of PCS is that the user's telephone number becomes his Personal Communication Number (PCN), which is "tied" to the user himself, and not to his phone or radio modem. A user traveling around the world with the PCS can freely receive phone calls and e-mails on their PCN.

Cellular communications were originally created for use in automobiles, while personal communications meant great possibilities. Compared to traditional cellular communications, PCS has several advantages. First, it is completely digital, which enables faster data transfer rates and facilitates the use of data compression technologies. Secondly, the frequency range used for the PCS (1850-2200 MHz) reduces the cost of the communication infrastructure. (Since the overall dimensions of the PCS base station antennas are smaller than the overall dimensions of the cellular base station antennas, they are cheaper to manufacture and install).

In theory, the US mobile system operates in two frequency bands - 824 and 894 MHz; PCS operates at 1850 and 1990 MHz. And since this service is based on the TDMA standard, the PCS has 8 timeslots and the channel spacing is 200KHz, as opposed to the usual three timeslots and 30KHz between channels.

3G is the latest technology in mobile communications. 3G means the phone belongs to the third generation - the first generation is analog mobile phones, the second is digital. 3G technology is used in multimedia mobile phones, commonly referred to as smartphones. These phones have multiple bands and high speed data transmission.

3G uses several mobile standards. The most common are three of them:

CDMA2000 is a further development of the 2nd generation CDMA One standard.
WCDMA (Wideband Code Division Multiple Access - broadband CDMA) is the radio interface technology chosen by most cellular operators to provide broadband radio access to support 3G services.
TD-SCDMA (English Time Division - Synchronous Code Division Multiple Access) is a Chinese standard for third generation mobile networks.

The 3G network can transfer data at speeds up to 3 Mb / s (therefore, in order to download an MP3 song of 3 minutes duration, it takes only about 15 seconds). For comparison, let's take second generation mobile phones - the fastest 2G phone can reach data transfer rates up to 144 Kb / s (it takes about 8 hours to download a 3-minute song). High-speed 3G data transfer is ideal for downloading information from the Internet, sending and receiving large multimedia files. 3G phones are a kind of mini-laptops that can handle large applications such as receiving streaming video from the Internet, sending and receiving faxes, and downloading e-mail messages with applications.

Of course, this requires base stations that transmit radio signals from phone to phone.

Mobile phone base stations are cast metal or lattice structures that rise hundreds of feet. This picture shows a modern tower that "serves" 3 different mobile operators. If you look at the base of the base stations, you can see that each mobile operator has installed their own equipment, which nowadays takes up very little space (at the base of older towers, small rooms were built for such equipment).

Base station. photo from the site http://www.prattfamily.demon.co.uk

A radio transmitter and receiver are placed inside such a block, thanks to which the tower communicates with mobile phones. The radio receivers are connected to the antenna on the tower with several thick cables. If you look closely, you will notice that the tower itself, all cables and equipment of the companies at the base of the base stations are well grounded. For example, the plate with the green wires attached to it is the copper ground plate.

In a mobile phone, as in any other electronic device, problems may occur:

Most often, these include corrosion of parts caused by moisture entering the device. If the phone gets wet, make sure the phone is completely dry before turning it on.
Excessive temperatures (eg in a car) can damage the battery or the electronic board of the phone. If the temperature is too low, the screen may turn off.
Analog mobile phones often face the problem of "cloning". A phone is considered "cloned" when someone intercepts its identification number and can call other numbers for free.

Here's how "cloning" works: Before calling anyone, your phone sends its ESN and MIN codes to the network. These codes are unique and it is thanks to them that the company knows who to send invoices for calls. When your phone transmits MIN / ESN codes, someone can hear (using a special device) and intercept them. If these codes are used in another mobile phone, then you can call from it completely free of charge, since the owner of these codes will pay the bill.

Communication of mobile, or, as they are also called, cell phones, is carried out not using wires, as in a conventional telephone system, but through radio waves. To make a call on a mobile phone, you need to dial the number as usual. Thereby, the radio message arrives at the base station operated by the cellular telephone company.

At a station that serves all calls within a given radius or zone, the controller device detects a call to a free radio channel. In addition, it routes the signal to the cellular telephone exchange. By reading the special codes transmitted by the phone,

ATS monitors the movement of a car in the area of \u200b\u200bthe first station. If during a call the machine bypasses a zone and enters the next one, the call is automatically transferred to the base station operating in that zone. When making a mobile phone call, the caller connects to an automatic cellular telephone exchange, which locates the mobile phone, requests a free radio channel from the circuit controller, and communicates — through the base station — with the desired number. Then the cell phone rings. When the driver picks up the phone, the circuit is complete.

Base station operation

Each base station receives signals emitted within a radius of three to six miles. To avoid noise, base stations with coincident boundaries must operate on different frequency channels. But even within the same city, stations that are sufficiently remote from each other can easily operate on the same channel.

The local telephone system, which serves both homes and offices, is based on wires running under and above the ground and connected to an automatic station.

Location and channel

The automatic telephone exchange locates the moving vehicle while the circuit controller routes the call to the communication channel.

Call area

When the car leaves the area of \u200b\u200bthe farthest base station, the driver can no longer use cellular communications. If a call is made on its way to the border of the zone, the signal gets weaker and weaker and eventually disappears completely.

On the way from station to station

Throughout a mobile call, an automatic telephone exchange for cellular communication fixes the location of a moving vehicle by the strength of the radio signals emanating from it. When the signal becomes too weak, the automatic telephone exchange alerts the base station, which in turn hands over the call to service the neighboring station.

Once, a friend who works as an engineer for a cellular operator offered to arrange a tour of the skyscrapers of Belgorod and talk about how cellular communication works. I, of course, could not refuse such a thing, and this review became the most interesting that I have seen recently, not to mention the fact that incredibly beautiful views of my hometown open up from these rooftops. Before starting this story, I want to sincerely thank Kirill for organizing this excursion and for technical advice in the process of writing this article.

The first roof was a skyscraper on Kostyukov Street next to the Vladimirsky residential complex. This 18-storey building stands on a hill, thus being one of the highest points in the city.

In any city, the roofs of high-rise buildings are always chosen by mobile operators - there are many antennas installed here.

These antennas are of two types. Panel rectangular, marshmallow-like antennas for cellular communications, or "sectors". Through them, your cell phone or modem communicates with the control unit - the base station. Usually, several sector antennas connected to one base station are installed at different angles to provide subscribers with communication from all sides. For optimal coverage (both technically and economically), base stations are positioned in such a way that their layout resembles a honeycomb - hence the term "cellular". In reality, of course, ideal cells are rarely obtained, since their location is influenced by many other factors, such as the relief, the possibility of installing the BS and the number of subscribers. Sector antennas are also installed directly in buildings to provide a signal inside them. In particular, indoor sectors are installed inside various Belgorod shopping and entertainment centers (City-Molle, Mega-Grinn, Rio, etc.), otherwise your mobile phones would not catch the network there.

Round antenna - radio relay (RRL). With the help of such antennas, communication is carried out between base stations, if there is no other communication between them. Such a connection is called a radio relay span. When installing 2 antennas, it is very important that they are clearly pointed at each other (this process is called alignment), because at the slightest deviation, the signal becomes worse, reducing the bandwidth. Antennas can be of different diameters (from 30 cm to two and a half meters) and operate in different frequency ranges (depending on the span, type of terrain and operator requirements).

The base station is the room in which the equipment is located. It can be a container, a partition in a building, and occasionally a heating cabinet. The container is supplied with an external 3-phase power supply of 380 volts. Electricity goes to the lead-in panel, from which AC consumers are powered (air conditioners and fire and security alarms). A UPS (uninterruptible power supply) is powered from the main board, which converts AC to DC at 48 volts, from which most of the base station equipment operates. In the photo - equipment racks and UPS of the GSM base station.

Stand of the GSM base station inside.

Uninterruptable power source. The base station and the transport network equipment (internal blocks of radio relay antennas, multiplexers, etc.) must have different power sources, since when the power is turned off, the transport network equipment must "hold out" longer.

The base station is the lowest level in the network hierarchy. Several dozen geographically connected stations are connected via a cable to the BSC (Base Station Controller), which monitors their performance and many processes, such as handover (switching a subscriber from one station to another without breaking the connection), updating the location and signaling, as well as work parameters. Controller cabinet.

Controller hardware.

Optical trunk multiplexer (a device that combines several different data streams for transmission over a single communication line).

BSC is a serious transport hub with a bunch of radio relay, optical equipment, critical to the quality of power supply, which is why, in the event of a power failure, it is equipped with serious batteries (pictured) or a diesel generator set (diesel generator).

The core of the network in a particular city or region, to which the base station controllers are connected, is the MSC (Mobile Switching Center) - an automatic telephone exchange or switch. It is MSC that determines where to send calls, as well as processes calls from external networks (city, other operators) and sends information about the duration of calls and ordered services to the billing center. A multi-level network structure is necessary for a more even load - after all, if the MSC, for example, had to perform the handover function and other functions of the base station controller, the load on it would increase significantly. For the core networks laid between the regions, fiber-optic cables are used, which allow instantaneous transmission of huge data streams.

The familiar word "SIM" comes from the English abbreviation SIM (Subscriber Identity Module, subscriber identification module). Each card has an IMSI (International Subscriber Identification Number, the international subscriber identification number, the same long number that is written on it in small numbers). When you turn on the phone, it transmits this number to the BS, from where it then goes to the BSC and then to the MSC. MSC asks the operator's database (HLR) about the presence of such a subscriber, and whether it is possible for him to provide communication services (whether he paid, whether they are connected), and then registers it in the VLR - a temporary database of subscribers located in the coverage area of \u200b\u200bthis MSC (this includes both subscribers of this network, and roamers - subscribers of other networks, currently connected to it).

GSM (originally derived from Groupe Spécial Mobile) is a mobile communication standard developed in Europe, which has actually become a global one (although there are other standards, such as CDMA, which is popular in America). This standard was focused primarily on voice data transmission. Third generation networks (UMTS), which are sometimes called 3GSM to indicate continuity and which use the HSDPA protocol, which significantly increases the transmission speed, are already more tailored specifically for data, although in the absence of a GSM network, you can still make a call via 3G. As for LTE, a 4th generation network, it is fully optimized for high-speed data transmission (although in Russian realities, much depends on the development of the so-called "transport network" by operators - a set of resources and capabilities for transferring large amounts of information and distributing these volumes for base stations).

The photo below is an LTE base station. In the event of a power outage, the batteries will last for another 5 hours.

A big obstacle to the development of high-speed mobile Internet in Russia is the shortage of radio frequencies. You cannot just install the equipment and start servicing, you must first get permission to use the frequency. However, the frequencies required to deploy such networks are often reserved by the Department of Defense in accordance with the standards of the 60-70s of the last century, when equipment needed wide ranges. Allocation (“conversion”) of such frequencies for civilian use is an expensive and complicated procedure, both technically and bureaucratic. In addition, until December 2013 in Russia, according to the law, frequencies were allocated only for specific technologies, and if a company received a frequency on which it was allowed to provide GSM communication services, it had no right to use the same frequency for LTE. Because of this, for example, Tele2, which at one time did not receive a separate frequency for 3G and 4G, for a long time could not start providing high-speed mobile Internet services.

Let's digress a little from the technical side, and look around. From this house, the city can be seen at a glance. Let's look at the very center. In the middle - the building of the city administration. The Transfiguration Cathedral looks out from behind it. The diorama "Fire arc" and the art museum, the park named after Lenin are visible.

The monument to Prince Vladimir from here seems quite tiny.

Buildings of BelSU.

Train station and city beach.

"Technologist", districts of Old Town and Kreida are visible in the distance.

The courtyard of the residential complex "Vladimirsky".

Gotta get a bow

And of course, panoramas. Belgorod, what a beauty!

With a closer look (unfortunately the weather was not ideal, although the sun was shining, the air was covered with haze, despite the raised contrast, it was not very clear to see.

Looking south from the same roof. The southern half of the city is popularly called "Kharkov Mountain".

The next object we visited was a 70-meter cell tower not far from BSTU.

There are antennas on the tower, and base station equipment in metal booths. The tower itself is surrounded by a barbed wire fence to prevent people from climbing.

To climb the tower, you need to be in good physical shape. Although I go to the gym all the time, in the end I started to get tired. And Cyril, who is a hefty jock himself, offered to imagine what it would be like to climb on it, also carrying heavy equipment.

But in general, the climb process itself was pretty good. It's great. There is no insurance - hold on tight.

An unused Soviet radio relay antenna installed back in the 1970s, which is too difficult to dismantle due to its weight and dimensions, so it continues to hang here. This particular tower is quite old and was built back in those days, however, most of the towers that we meet appeared already during the rapid development of cellular communications in Russia.

The installation of such towers is usually carried out using a helicopter. The assembled parts of the structure weighing 2-3 tons each are brought to the site on long tractors, after which the machine lifts them, and the installers fix them. Red and white coloring, increasing the visibility of the structure for aircraft, is a requirement spelled out in the Manual for the operation of civil airfields of the Russian Federation. This paint is applied to all high-rise structures, masts and factory pipes.

At the top of the tower, as in the skyscrapers, there are red lights of the light barriers, which are needed for the same purposes as the painting, but in the dark.

As a rule, equipment from several companies is located on one tower. The tower itself, at the same time, can belong to only one operator (while others pay rent), or several, or even belong to some other organization that does not engage in communication services, but only leases the object. Recently, sharing of base stations has also begun to appear in Russia.

The tower sways a little in the wind - it should be so.

I want to become a base player more and more.

New-2 microdistrict under construction and garages, from above, reminiscent of the slums of some Latin American city. A separate garage cooperative next to a residential area is such a purely Soviet invention that is perplexing in the West.

Gubkin Street, Khargora.

A little further in the middle, the buildings of the BSTU are visible. On the right in the distance is the city beach. At the top left is the skyscraper we were just at.

General view from the roof of the building. In the leftmost part - the beginning of the Bolkhovets district and the western industrial zone (the yellow spot on the horizon is a cement plant quarry). Levoberezhye area, Khorkina center (blue building), BelSU, Victory Park, Suprunovka area built up with cottages, railway, Salyut area, two city TV towers, Shchorsa street (it would be more correct to call it avenue), Sfera shopping center, Pervomaisky district ...

Victory Park and the central part of the city, Suprunovka.

Shchors Street.

Two city TV towers - old (left) and new. They are beautifully illuminated at night. It is very, very difficult to get on them (unless you are Vadim Makhorov).

Plekhanov and Horovets Streets.

Western industrial zone (cement plant, Energomash, Belatsi).

One of the disadvantages of Belgorod is that there are almost no historical sights here, which makes it of little interest for tourists. Pre-revolutionary buildings are dotted in the center, but they are surrounded on all sides by modern ones. There is not a single old street like in cities like Tula, Yaroslavl or Vladimir, except for a couple of streets with Stalinist architecture. Now the entire center is being built up with glass-concrete high-rises, and other areas entirely consist of such high-rise buildings. The panel houses in the foreground are typical of the 80s, those further on are typical modern architecture of Belgorod sleeping areas.

Ceramic cladding of buildings. In addition to new houses, it is often used for the restoration of buildings from the era of Khrushchev and Brezhnev - square buildings, which two years after whitewashing begin to look shabby, being faced, look quite modern and aesthetically pleasing.

Ventilation.

In conclusion, we climbed to the roof of the former Electrocontact plant. In Soviet times, the plant produced various electrical equipment, but in the nineties it was closed due to unprofitability. Now its buildings house offices and shops, workshops are used as warehouses or are empty.

There are radio masts on the roof of one of the buildings.

Such a cozy roof.

Nearby is one of the city's attractions, a wooden church of the holy martyrs Faith, Nadezhda, Lyubov and their mother Sophia. In 2009 epic burned out , but since then it has been rebuilt.

The roofs of the workshops resemble the streets of an abandoned village. I wonder how you can get there?

Gorky Street and the Shchors-Korolev-Gorky ring.

I'm not afraid to say that in terms of cognition, this was the most interesting excursion since visiting the Exclusion Zone 6 years ago. More than anything else, I adore industrial insider excursions, when you can look at what is next to us, closely connected with our life, but at the same time little known and closed to a person from the street.

Visited Dubovoy (a suburb of Belgorod south of Khargora). Hi, Nastya:-)

Such a quiet and pleasant sleeping area. Most of it is occupied by cottages.

This year, a ski complex, which had been under construction for a very long time, finally started working (though, judging by the reviews, it was rather conditional).

If you come to the pedestrian bridge over the private sector dividing the northern and southern parts of the city in the evening, you can meet the Lady of the Goats. Can she be included in the list of urban madmen?

Pleasure boats on Vezelka.

Why are modern graduates so big? At the age of 17, I weighed 55 kilograms, and then you look - just some uncles and aunts. Probably, the hungry nineties, in which we grew up, are to blame :-)

Usually, the sight of the sun setting behind Belgorod University is associated with J: Morse's song “Pavetra”, but at that moment it was strange to realize that summer had not even begun yet, although “Spring”, “Vopliv Vidoplyasova,” which was firmly attached to last April, is also here it didn’t fit ... It would be interesting to understand why I have such a desire to tie soundtracks to everything.

I float with you there, de lito, there, de lito,
There, de my soul, go over the edge.
I float with you there, de lito, there, de lito,
There, de my soul, carry me beyond the sky.

With us years it was added and changed,
We had a warmth with us,
And during the evening it was so uncomfortable
Blue sky with gold and wine ©